package builder

import (
	"bytes"
	"fmt"
	"regexp"
	"strings"
)

// **What failed is picked from the whole of a check's output, as it streams** (novox/hq issue 460).
//
// A repository's own check kept only the last reportLines lines of what it printed, and named what failed
// from those. A long store-backed run prints its logs after the failure: the `--- FAIL:` line of mesh-controller
// #218 was pushed out of the tail by the package's own log lines, and the verdict said only
// "FAIL <package> 268.072s" — the test that failed could not be named, and the fix was a guess. #220's failure
// came a few dozen lines before the end, inside the tail, and was named. The length of what came after the
// failure decided it, nothing else.
//
// So every line is looked at as it is written, and the lines that name what failed are kept whole, wherever
// in the output they are: each `--- FAIL:` line with its indented message lines, a `panic:` with its first
// frames, a `WARNING: DATA RACE` report, each `FAIL\t<package>` line, a build error with its package, and
// the files gofmt lists. The rest is cut as before.

// Bounds on what is picked, so a run that fails everywhere still travels in a verdict: the controller cuts a
// report to its last 60 KiB (maxCheckReport), and what failed is said at the report's end, so it stays inside.
const (
	// failureLines and failureBytes bound everything picked from one run.
	failureLines = 400
	failureBytes = 32 << 10
	// failureLineBytes bounds one picked line: a message that pastes a whole document is cut, said.
	failureLineBytes = 1 << 10
	// The lines kept after the line that opens each kind of block.
	failMessageLines = 30 // a --- FAIL's messages
	panicLines       = 40 // a panic's first frames
	raceLines        = 80 // a data race report, to its closing rule
	buildLines       = 40 // a package's build errors
	gofmtLines       = 50 // the files gofmt lists
	// failedNames bounds how many further failing tests the summary names after the first.
	failedNames = 5
)

// goError is a compiler's or vet's line: a Go file, a line, and what is wrong there.
var goError = regexp.MustCompile(`^\S+\.go:\d+(:\d+)?: `)

// raceRule is the line the race detector opens and closes its report with.
const raceRule = "=================="

type failureBlock int

const (
	noBlock failureBlock = iota
	inFail
	inPanic
	inRace
	inBuild
	inGofmt
)

// failures keeps the lines of a check's output that name what failed. It is an io.Writer, fed the same
// bytes as the report's tail.
type failures struct {
	partial []byte
	kept    []string
	size    int
	dropped int

	block    failureBlock
	indent   int // a --- FAIL line's indentation: its messages are indented deeper
	left     int // lines the open block may still keep
	headers  []string
	tests    []string // every failing test's --- FAIL line, in order
	lastRule bool     // the line before was the race detector's rule, which opens its report
}

func (f *failures) Write(p []byte) (int, error) {
	f.partial = append(f.partial, p...)
	for {
		i := bytes.IndexByte(f.partial, '\n')
		if i < 0 {
			break
		}
		f.line(strings.TrimRight(string(f.partial[:i]), "\r"))
		f.partial = f.partial[i+1:]
	}
	// A line with no end, longer than any line is kept, is judged by its start.
	if len(f.partial) > failureLineBytes*4 {
		f.line(string(f.partial))
		f.partial = nil
	}
	return len(p), nil
}

// flush judges what is left of a last line with no newline.
func (f *failures) flush() {
	if len(f.partial) > 0 {
		f.line(strings.TrimRight(string(f.partial), "\r"))
		f.partial = nil
	}
}

func indentOf(line string) int {
	return len(line) - len(strings.TrimLeft(line, " \t"))
}

func (f *failures) keep(line string) {
	if f.size >= failureBytes || len(f.kept) >= failureLines {
		f.dropped++
		return
	}
	if len(line) > failureLineBytes {
		line = line[:failureLineBytes] + fmt.Sprintf(" … (%d bytes more)", len(line)-failureLineBytes)
	}
	f.kept = append(f.kept, line)
	f.size += len(line) + 1
}

func (f *failures) open(block failureBlock, lines int) {
	f.block, f.left = block, lines
}

func (f *failures) line(line string) {
	trimmed := strings.TrimSpace(line)
	rule := trimmed == raceRule

	// A line that opens a block ends whatever block was open.
	if f.opens(line, trimmed) {
		f.lastRule = rule
		return
	}
	switch f.block {
	case inFail:
		if trimmed != "" && indentOf(line) > f.indent && f.left > 0 {
			f.left--
			f.keep(line)
			f.lastRule = rule
			return
		}
	case inPanic:
		if f.left > 0 && !strings.HasPrefix(line, "FAIL") && !strings.HasPrefix(line, "ok  \t") &&
			!strings.HasPrefix(line, "exit status") {
			f.left--
			f.keep(line)
			f.lastRule = rule
			return
		}
	case inRace:
		if f.left > 0 {
			f.left--
			f.keep(line)
			if rule {
				f.block = noBlock
			}
			f.lastRule = rule
			return
		}
	case inBuild:
		if f.left > 0 && trimmed != "" && !strings.HasPrefix(line, "FAIL") && !strings.HasPrefix(line, "ok  \t") &&
			!strings.HasPrefix(line, "?   \t") {
			f.left--
			f.keep(line)
			f.lastRule = rule
			return
		}
	case inGofmt:
		if f.left > 0 && trimmed != "" {
			f.left--
			f.keep(line)
			f.lastRule = rule
			return
		}
	}
	f.block = noBlock

	switch {
	case strings.HasPrefix(line, "# "):
		// A package's name before its build errors — kept only when an error follows it.
		f.headers = append(f.headers, line)
		if len(f.headers) > 4 {
			f.headers = f.headers[1:]
		}
	case len(f.headers) > 0 && goError.MatchString(line):
		for _, h := range f.headers {
			f.keep(h)
		}
		f.headers = nil
		f.keep(line)
		f.open(inBuild, buildLines)
	case strings.HasPrefix(line, "FAIL\t"):
		f.headers = nil
		f.keep(line)
	default:
		f.headers = nil
	}
	f.lastRule = rule
}

// opens keeps a line that opens a block of what failed, and opens the block. False for any other line.
func (f *failures) opens(line, trimmed string) bool {
	switch {
	case strings.HasPrefix(trimmed, "--- FAIL:"):
		f.headers = nil
		f.keep(line)
		f.tests = append(f.tests, trimmed)
		f.indent = indentOf(line)
		f.open(inFail, failMessageLines)
	case strings.HasPrefix(line, "panic:") || strings.HasPrefix(line, "fatal error:"):
		f.headers = nil
		f.keep(line)
		f.open(inPanic, panicLines)
	case trimmed == "WARNING: DATA RACE":
		f.headers = nil
		if f.lastRule {
			f.keep(raceRule)
		}
		f.keep(line)
		f.open(inRace, raceLines)
	case strings.HasPrefix(trimmed, "not gofmt'd:"):
		f.headers = nil
		f.keep(line)
		f.open(inGofmt, gofmtLines)
	default:
		return false
	}
	return true
}

// String is every line picked, in the order the run printed them, and how many more were left out.
func (f *failures) String() string {
	f.flush()
	s := strings.Join(f.kept, "\n")
	if f.dropped > 0 {
		s += fmt.Sprintf("\n… %d more line(s) naming what failed, past the %d lines or %d KiB kept", f.dropped,
			failureLines, failureBytes>>10)
	}
	return s
}

// said is what the repository layer's summary says failed: the first thing that failed, whole, then the
// further failing tests by name. Empty when nothing was picked.
func (f *failures) said() string {
	picked := f.String()
	if picked == "" {
		return ""
	}
	first := whatFailed(picked)
	var more []string
	for _, t := range f.tests {
		if t == first {
			continue
		}
		// A subtest's parent fails with it; its name is in the subtest's.
		name := strings.Fields(strings.TrimPrefix(t, "--- FAIL:"))
		if len(name) > 0 {
			more = append(more, name[0])
		}
	}
	more = withoutParents(more)
	switch {
	case len(more) == 0:
		return first
	case len(more) > failedNames:
		return fmt.Sprintf("%s; and %s and %d more", first, strings.Join(more[:failedNames], ", "),
			len(more)-failedNames)
	default:
		return first + "; and " + strings.Join(more, ", ")
	}
}

// withoutParents drops a test whose subtest is also named.
func withoutParents(names []string) []string {
	var out []string
	for _, n := range names {
		parent := false
		for _, m := range names {
			if strings.HasPrefix(m, n+"/") {
				parent = true
				break
			}
		}
		if !parent {
			out = append(out, n)
		}
	}
	return out
}