package main

import (
	"context"
	"encoding/base64"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"unicode/utf8"
)

// gitea_commit (novox/hq issue 375): one commit on a branch of its own, so an agent follows the branch / pull
// request / approval rule without anyone pushing by hand. By the rule gitea_api already enforces for a file
// written (novox/hq ADR 0266): never the repository's default branch, never a branch a protection rule names.
// Nothing about merging changes — that still needs a review at the head and both required checks green
// (gitea_merge_pull_request).

// FileChange is one file of a commit: its new content, as text or base64, or its deletion.
type FileChange struct {
	Path          string
	Content       *string
	ContentBase64 *string
	Delete        bool
}

// CommitAsk is one gitea_commit call.
type CommitAsk struct {
	Owner, Repo string
	Branch      string
	Base        string // the branch or commit a new branch starts from; the default branch when empty
	Message     string
	Files       []FileChange
	Patch       string // a unified diff, as git diff writes it, instead of Files
}

// Committed is what gitea_commit made.
type Committed struct {
	Repository string          `json:"repository"`
	Branch     string          `json:"branch"`
	Created    bool            `json:"created"`
	Base       string          `json:"base,omitempty"`
	Parent     string          `json:"parent"`
	Commit     string          `json:"commit"`
	Files      []CommittedFile `json:"files,omitempty"`
	Said       []string        `json:"said"`
}

// CommittedFile is one file the commit changed, and how.
type CommittedFile struct {
	Path      string `json:"path"`
	Operation string `json:"operation"`
}

// What one commit carries at most (novox/hq issue 539): files, one file's content, one patch, and every
// file's content together, in bytes as committed (content_base64 decoded). Larger work is several commits.
const (
	maxFiles       = 200
	maxFileBytes   = 4 << 20
	maxPatchBytes  = 4 << 20
	maxCommitBytes = 16 << 20
)

// readCommitAsk reads the tool's arguments.
func readCommitAsk(args map[string]any) (CommitAsk, error) {
	a := CommitAsk{Owner: text(args, "owner"), Repo: text(args, "repo"), Branch: text(args, "branch"),
		Base: text(args, "base"), Message: strings.TrimSpace(raw(args, "message"))}
	a.Patch = raw(args, "patch")
	if a.Branch == "" {
		return a, refuse("branch is required: the branch the commit goes on, a branch of its own (created from base when absent). Nothing was sent")
	}
	if a.Message == "" {
		return a, refuse("message is required: the commit's message. Nothing was sent")
	}
	files, given := args["files"]
	if given && files != nil {
		list, ok := files.([]any)
		if !ok {
			return a, refuse("files is a list of {path, content | content_base64 | delete: true}. Nothing was sent")
		}
		for i, item := range list {
			m, ok := item.(map[string]any)
			if !ok {
				return a, refuse("files[%d] is not an object {path, content | content_base64 | delete: true}. Nothing was sent", i)
			}
			fc := FileChange{Path: text(m, "path")}
			if v, ok := m["content"]; ok && v != nil {
				s, ok := v.(string)
				if !ok {
					return a, refuse("files[%d].content is text. Nothing was sent", i)
				}
				fc.Content = &s
			}
			if v, ok := m["content_base64"]; ok && v != nil {
				s, ok := v.(string)
				if !ok {
					return a, refuse("files[%d].content_base64 is text. Nothing was sent", i)
				}
				fc.ContentBase64 = &s
			}
			if v, ok := m["delete"]; ok && v != nil {
				b, ok := v.(bool)
				if !ok {
					return a, refuse("files[%d].delete is true or false. Nothing was sent", i)
				}
				fc.Delete = b
			}
			a.Files = append(a.Files, fc)
		}
	}
	switch {
	case len(a.Files) == 0 && strings.TrimSpace(a.Patch) == "":
		return a, refuse("give files (each {path, content | content_base64 | delete: true}) or patch (a unified diff, as git diff writes it). Nothing was sent")
	case len(a.Files) > 0 && strings.TrimSpace(a.Patch) != "":
		return a, refuse("give files or patch, not both: one commit carries one of them. Nothing was sent")
	case len(a.Files) > maxFiles:
		return a, refuse("%d files is more than the %d one commit carries. Nothing was sent", len(a.Files), maxFiles)
	case len(a.Patch) > maxPatchBytes:
		return a, refuse("the patch is %s, more than the %s one commit carries: split it into several commits. Nothing was sent", mib(len(a.Patch)), mib(maxPatchBytes))
	}
	seen := map[string]bool{}
	total := 0
	for i, fc := range a.Files {
		if strings.HasPrefix(fc.Path, "/") {
			return a, refuse("files[%d].path %q is relative to the repository's root, without a leading slash. Nothing was sent", i, fc.Path)
		}
		if _, err := segments("file path", fc.Path); err != nil {
			return a, err
		}
		if seen[fc.Path] {
			return a, refuse("%s is named twice in files. Nothing was sent", fc.Path)
		}
		seen[fc.Path] = true
		given := 0
		for _, g := range []bool{fc.Content != nil, fc.ContentBase64 != nil, fc.Delete} {
			if g {
				given++
			}
		}
		if given != 1 {
			return a, refuse("files[%d] (%s) needs exactly one of content, content_base64 or delete: true. Nothing was sent", i, fc.Path)
		}
		if fc.Content != nil && !utf8.ValidString(*fc.Content) {
			return a, refuse("files[%d].content (%s) is not UTF-8 text: give it as content_base64. Nothing was sent", i, fc.Path)
		}
		size := 0
		switch {
		case fc.Content != nil:
			size = len(*fc.Content)
		case fc.ContentBase64 != nil:
			if base64.StdEncoding.DecodedLen(len(*fc.ContentBase64)) > maxFileBytes+3 {
				size = base64.StdEncoding.DecodedLen(len(*fc.ContentBase64))
				break
			}
			raw, err := base64.StdEncoding.DecodeString(*fc.ContentBase64)
			if err != nil {
				return a, refuse("files[%d].content_base64 (%s) is not base64: %v. Nothing was sent", i, fc.Path, err)
			}
			size = len(raw)
		}
		if size > maxFileBytes {
			return a, refuse("files[%d] (%s) is %s, more than the %s one file of a commit may be. Nothing was sent", i, fc.Path, mib(size), mib(maxFileBytes))
		}
		total += size
	}
	if total > maxCommitBytes {
		return a, refuse("the files are %s together, more than the %s one commit carries: split them into several commits. Nothing was sent", mib(total), mib(maxCommitBytes))
	}
	return a, nil
}

// mib says a size in bytes in MiB, to a tenth.
func mib(n int) string { return fmt.Sprintf("%.1f MiB", float64(n)/(1<<20)) }

// targetRefused says why a commit may not go on a branch: the default branch, or one a protection rule names.
func targetRefused(target, defaultBranch string, rules []Protection) error {
	if target == defaultBranch {
		return refuse("a commit on %s, the repository's default branch, is refused: a change reaches it by a pull request "+
			"that passes its checks (novox/hq ADR 0266). Put it on a branch of its own. Nothing was sent", target)
	}
	var guarding []string
	for _, r := range rules {
		if n := r.name(); n != "" && ruleCovers(n, target) {
			guarding = append(guarding, n)
		}
	}
	if len(guarding) > 0 {
		return refuse("a commit on %s is refused: the protection rule %s guards it (novox/hq ADR 0266). Put it on a "+
			"branch of its own. Nothing was sent", target, strings.Join(guarding, ", "))
	}
	return nil
}

// commit puts one commit on the asked branch, after the judgement, and reads the branch back.
func commit(ctx context.Context, f *Forge, a CommitAsk) (*Committed, error) {
	repo, err := repoPath(a.Owner, a.Repo)
	if err != nil {
		return nil, err
	}
	if _, err := segments("branch", a.Branch); err != nil {
		return nil, err
	}
	var r Repo
	if err := f.GetJSON(ctx, repo, &r); err != nil {
		return nil, err
	}
	if r.DefaultBranch == "" {
		return nil, fmt.Errorf("the forge did not say %s/%s's default branch, so whether %s is it cannot be judged. Nothing was sent", a.Owner, a.Repo, a.Branch)
	}
	// Read the rules, or refuse: a branch the rules could not be read for is never written (fails closed).
	var rules []Protection
	if err := f.GetJSON(ctx, repo+"/branch_protections", &rules); err != nil {
		return nil, fmt.Errorf("the protection rules of %s/%s could not be read, so the commit was not judged and nothing was sent: %w", a.Owner, a.Repo, err)
	}
	if err := targetRefused(a.Branch, r.DefaultBranch, rules); err != nil {
		return nil, err
	}

	out := &Committed{Repository: a.Owner + "/" + a.Repo, Branch: a.Branch}
	existing, err := f.branch(ctx, repo, a.Branch)
	if err != nil {
		return nil, err
	}
	// The files are judged at the commit just read, never at a branch name that could move between two
	// reads (novox/hq issue 539): a file the branch changes meanwhile is refused by the forge, whose update
	// and delete carry the blob read here.
	var ref string
	if existing != nil {
		out.Parent = existing.Commit.ID
		ref = existing.Commit.ID
		if a.Base != "" {
			out.Said = append(out.Said, fmt.Sprintf("%s exists, at %s: base %s was not used", a.Branch, short(existing.Commit.ID), a.Base))
		}
	} else {
		out.Created = true
		out.Base = a.Base
		if out.Base == "" {
			out.Base = r.DefaultBranch
		}
		b, err := f.branch(ctx, repo, out.Base)
		if err != nil {
			return nil, err
		}
		if b == nil {
			return nil, refuse("%s does not exist, and its base %s is not a branch of %s/%s. Nothing was sent", a.Branch, out.Base, a.Owner, a.Repo)
		}
		out.Parent = b.Commit.ID
		ref = b.Commit.ID
	}

	// Where the forge takes the commit: on the branch, or on a new one from the base's commit.
	on := map[string]any{"message": a.Message}
	if out.Created {
		on["branch"] = out.Base
		on["new_branch"] = a.Branch
	} else {
		on["branch"] = a.Branch
	}

	// The forge takes no commit to build on, only a branch (Gitea 1.27: neither /contents nor /diffpatch
	// carries a last commit), so the parent is read from what it made, never assumed (novox/hq issue 539).
	var made struct {
		Commit madeCommit `json:"commit"`
	}
	if a.Patch != "" {
		on["content"] = a.Patch
		if err := f.SendJSON(ctx, http.MethodPost, repo+"/diffpatch", on, &made); err != nil {
			return nil, fmt.Errorf("the forge did not take the patch: %w", err)
		}
	} else {
		var ops []map[string]any
		for _, fc := range a.Files {
			sha, err := f.blobAt(ctx, repo, fc.Path, ref)
			if err != nil {
				return nil, err
			}
			op := map[string]any{"path": fc.Path}
			switch {
			case fc.Delete && sha == "":
				return nil, refuse("%s is to be deleted, but %s has no such file at %s. Nothing was sent", fc.Path, a.Owner+"/"+a.Repo, short(ref))
			case fc.Delete:
				op["operation"], op["sha"] = "delete", sha
			case sha == "":
				op["operation"] = "create"
			default:
				op["operation"], op["sha"] = "update", sha
			}
			if !fc.Delete {
				if fc.Content != nil {
					op["content"] = base64.StdEncoding.EncodeToString([]byte(*fc.Content))
				} else {
					op["content"] = *fc.ContentBase64
				}
			}
			ops = append(ops, op)
			out.Files = append(out.Files, CommittedFile{Path: fc.Path, Operation: op["operation"].(string)})
		}
		on["files"] = ops
		if err := f.SendJSON(ctx, http.MethodPost, repo+"/contents", on, &made); err != nil {
			return nil, fmt.Errorf("the forge did not take the commit: %w", err)
		}
	}
	if made.Commit.SHA == "" {
		return nil, fmt.Errorf("the forge answered the commit on %s without saying the commit it made: read the branch (gitea_list_branches) before trying again", a.Branch)
	}
	out.Commit = made.Commit.SHA
	read := out.Parent
	parent, err := f.parentOf(ctx, repo, made.Commit)
	if err != nil {
		return nil, fmt.Errorf("the forge made %s on %s, but which commit it went on could not be read: %w", out.Commit, a.Branch, err)
	}
	out.Parent = parent
	if parent != read {
		moved := "branch " + a.Branch
		if out.Created {
			moved = "base " + out.Base
		}
		how := "each file it changes was checked against " + short(read) + " by its blob, so none of them changed in between"
		if a.Patch != "" {
			how = "the forge applied the patch there, and it refuses a patch whose context changed"
		}
		out.Said = append(out.Said, fmt.Sprintf("the %s moved from %s to %s between the read and the commit, so the "+
			"commit went on %s: %s. What else changed in between: gitea_compare %s...%s",
			moved, short(read), short(parent), short(parent), how, short(read), short(parent)))
	}

	// Evidence over assertion: the branch is read back, and it must be at the commit the forge said.
	after, err := f.branch(ctx, repo, a.Branch)
	switch {
	case err != nil:
		return nil, fmt.Errorf("the forge made %s on %s, but the branch could not be read back: %w", out.Commit, a.Branch, err)
	case after == nil:
		return nil, fmt.Errorf("the forge said it made %s on %s, but the branch does not exist", out.Commit, a.Branch)
	case after.Commit.ID != out.Commit:
		return nil, fmt.Errorf("the forge said it made %s on %s, but the branch is at %s: something else moved it", out.Commit, a.Branch, after.Commit.ID)
	}
	what := "on"
	if out.Created {
		what = "on the new branch"
	}
	out.Said = append(out.Said, fmt.Sprintf("%s committed %s %s of %s, after %s; the branch is there now. A merge "+
		"still needs a review at this head and both required checks green", short(out.Commit), what, a.Branch, out.Repository, short(out.Parent)))
	return out, nil
}

// madeCommit is the commit the forge answers a write with.
type madeCommit struct {
	SHA     string `json:"sha"`
	Parents []struct {
		SHA string `json:"sha"`
	} `json:"parents"`
}

// parentOf is the commit the forge made its commit on: from its answer, or read from the commit when the
// answer does not say it.
func (f *Forge) parentOf(ctx context.Context, repo string, made madeCommit) (string, error) {
	if len(made.Parents) == 0 {
		var read madeCommit
		if err := f.GetJSON(ctx, repo+"/git/commits/"+url.PathEscape(made.SHA)+"?stat=false&verification=false&files=false", &read); err != nil {
			return "", err
		}
		made = read
	}
	if len(made.Parents) != 1 || made.Parents[0].SHA == "" {
		return "", fmt.Errorf("the forge says %s has %d parents, not one", made.SHA, len(made.Parents))
	}
	return made.Parents[0].SHA, nil
}

// blobAt is the blob sha of a file at a ref, "" when there is no file there.
func (f *Forge) blobAt(ctx context.Context, repo, path, ref string) (string, error) {
	seg, err := segments("file path", path)
	if err != nil {
		return "", err
	}
	var entry struct {
		Type string `json:"type"`
		SHA  string `json:"sha"`
	}
	var list []any
	body, err := f.Do(ctx, http.MethodGet, repo+"/contents/"+seg+"?ref="+queryEscape(ref), nil, maxBody)
	if err != nil {
		if errors.Is(err, errNotFound) {
			return "", nil
		}
		return "", err
	}
	if jsonInto(body, &list) == nil {
		return "", refuse("%s is a directory, not a file. Nothing was sent", path)
	}
	if err := jsonInto(body, &entry); err != nil {
		return "", fmt.Errorf("the forge's answer about %s is not readable: %w", path, err)
	}
	if entry.Type != "file" && entry.Type != "symlink" {
		return "", refuse("%s is a %s, not a file. Nothing was sent", path, entry.Type)
	}
	return entry.SHA, nil
}

func short(sha string) string {
	if len(sha) > 12 {
		return sha[:12]
	}
	return sha
}