package delivery

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"path"
	"regexp"
	"strings"
)

// **A run ask has a program built from a change and run in the build seat's sandbox** (novox/hq ADR 0644, ADR 0656;
// design 47, *What ADR 0656 leaves to this design*: the build seat's ask `run`; issue 1921). It goes on the Go seat's
// check stream, a whole job pulled where there is capacity, like a compose: the build module fetches Program at its
// commit and builds it once per RunKey, in a step that runs nothing but the build; fetches every head of Heads and lays
// each read-only under the directory RunHeadsEnv names, at its repository's path (`<owner>/<name>`); reads the input
// Input names, checks its digest and writes it to the file RunInputEnv names; then runs the program with Args, no
// network and no bus account (ADR 0448 §2, §4), and answers RunAnswer on its step key.
//
// The input is carried by reference, as a compose carries its manifests: the asker keeps it in a state of its own by its
// digest (RunInput), measured against RunInputBound before it asks, so a message on the bus never carries it (issue 1930).

// RunJob is a run ask's job.
type RunJob struct {
	// Program is where the program is built: the repository and full commit fetched, the Go module's directory in it and
	// the program's import path. The ask's Packages are the mesh package versions it builds against (ADR 0573 §2, §4).
	Program RunProgram `json:"program"`
	// Heads are the commits the program reads, each laid read-only at its repository's path; a repository at most once.
	Heads []RunHead `json:"heads"`
	// Input names the program's input, kept by the asker by its digest.
	Input RunInput `json:"input"`
	// Args are the program's arguments (a checking program's `-seats` or `-verdict`), each a word or a flag.
	Args []string `json:"args,omitempty"`
	// Reader names, for a reader of the ask, what the run is for ("checking program of mesh-delivery head").
	Reader string `json:"reader,omitempty"`
}

// RunProgram is where a run's program is built from.
type RunProgram struct {
	Repository string `json:"repository"`
	Commit     string `json:"commit"`
	Dir        string `json:"dir"`
	Package    string `json:"package"`
}

// RunHead is one commit a run's program reads.
type RunHead struct {
	Repository string `json:"repository"`
	Commit     string `json:"commit"`
}

// RunInput is a run's input by reference: the state it is kept in, named as a manifest's `reads` names a state
// (`<module>.<state>`), its key (the sha256 of its bytes, 64 lowercase hex digits) and its size in bytes.
type RunInput struct {
	State  string `json:"state"`
	Digest string `json:"digest"`
	Size   int    `json:"size"`
}

// RunInputBound is the most bytes a run's input may hold: under the bus's message limit, so the asker can keep it as
// one value.
const RunInputBound = 768 << 10

// RunHeadsEnv names, for the program, the directory its heads are laid in; RunInputEnv the file its input is written to.
const (
	RunHeadsEnv = "MESH_RUN_HEADS"
	RunInputEnv = "MESH_RUN_INPUT"
)

// RunInputOf is the reference to body kept in state, refusing a body over RunInputBound, naming its size, so an asker
// refuses it before asking.
func RunInputOf(state string, body []byte) (RunInput, error) {
	if len(body) > RunInputBound {
		return RunInput{}, fmt.Errorf("delivery: a run's input of %d bytes is over its bound of %d bytes", len(body), RunInputBound)
	}
	sum := sha256.Sum256(body)
	in := RunInput{State: state, Digest: hex.EncodeToString(sum[:]), Size: len(body)}
	return in, in.check("")
}

// Verify refuses body when it is not the input i names: another size or another digest.
func (i RunInput) Verify(body []byte) error {
	sum := sha256.Sum256(body)
	if len(body) != i.Size || hex.EncodeToString(sum[:]) != i.Digest {
		return fmt.Errorf("delivery: the input read from %s under %s is not the one the ask names (%d bytes, %d named)", i.State, i.Digest, len(body), i.Size)
	}
	return nil
}

var (
	runStateOK  = regexp.MustCompile(`^[a-z0-9][-a-z0-9]*\.[a-z0-9][-a-z0-9]*$`)
	runDigestOK = regexp.MustCompile(`^[0-9a-f]{64}$`)
	runArgOK    = regexp.MustCompile(`^[-=_./a-zA-Z0-9]+$`)
)

func (i RunInput) check(id string) error {
	switch {
	case !runStateOK.MatchString(i.State):
		return fmt.Errorf("delivery: the run ask %s keeps its input in %q, which is no <module>.<state>", id, i.State)
	case !runDigestOK.MatchString(i.Digest):
		return fmt.Errorf("delivery: the run ask %s names its input by %q, which is no sha256 digest", id, i.Digest)
	case i.Size <= 0 || i.Size > RunInputBound:
		return fmt.Errorf("delivery: the run ask %s names an input of %d bytes, outside 1 to %d", id, i.Size, RunInputBound)
	}
	return nil
}

func (r RunJob) check(id string) error {
	p := r.Program
	if err := checkRepository(p.Repository); err != nil {
		return fmt.Errorf("the run ask %s's program: %w", id, err)
	}
	if !askCommitOK.MatchString(p.Commit) {
		return fmt.Errorf("delivery: the run ask %s builds its program at no full commit", id)
	}
	if p.Dir == "" || p.Dir != path.Clean(p.Dir) || strings.HasPrefix(p.Dir, "/") || p.Dir == ".." || strings.HasPrefix(p.Dir, "../") {
		return fmt.Errorf("delivery: the run ask %s names no clean directory inside the repository (%q)", id, p.Dir)
	}
	if p.Package == "" || strings.ContainsAny(p.Package, " \t\n") {
		return fmt.Errorf("delivery: the run ask %s names no package to build (%q)", id, p.Package)
	}
	if len(r.Heads) == 0 {
		return fmt.Errorf("delivery: the run ask %s names no head", id)
	}
	seen := map[string]bool{}
	for _, h := range r.Heads {
		if err := checkRepository(h.Repository); err != nil {
			return fmt.Errorf("the run ask %s's head: %w", id, err)
		}
		if !askCommitOK.MatchString(h.Commit) {
			return fmt.Errorf("delivery: the run ask %s names the head of %s at no full commit", id, h.Repository)
		}
		if seen[h.Repository] {
			return fmt.Errorf("delivery: the run ask %s names %s twice", id, h.Repository)
		}
		seen[h.Repository] = true
	}
	for _, a := range r.Args {
		if !runArgOK.MatchString(a) {
			return fmt.Errorf("delivery: the run ask %s names the argument %q, which is no word or flag", id, a)
		}
	}
	return r.Input.check(id)
}

// RunAnswer is a run ask's step result: whether this run built the program or took the one kept under its key, the
// key, the program's exit, the last line of its standard output (Output, raw when it is JSON, else as a JSON string),
// and Said: the first line of its standard error, or why the step could not run it.
type RunAnswer struct {
	Built  bool            `json:"built"`
	Key    string          `json:"key"`
	Exit   int             `json:"exit"`
	Output json.RawMessage `json:"output,omitempty"`
	Said   string          `json:"said,omitempty"`
}

// RunKey is the key a build module keeps a built program under, as ComposerKey keeps a composer: what it was built
// from, the toolchain and the asked package versions, hashed (`program-` and 16 hex digits).
func RunKey(p RunProgram, toolchain ToolchainUsed, versions PackageVersions) string {
	return "program-" + strings.TrimPrefix(ComposerKey(p.Repository, p.Commit, p.Dir, p.Package, toolchain, versions), "composer-")
}