package workphase

import (
	"encoding/json"
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

// PlanDoc is a sealed markdown specification. The document is retained
// verbatim, because that is what an implement session receives: a plan
// flattened to bullet lines is a summary, and a summary cannot be executed.
//
// The parsed fields exist so Orchestra can act on the plan without rereading
// prose. Nothing outside this file interprets the markdown.
type PlanDoc struct {
	// Markdown is the exact bytes that were sealed.
	Markdown string `json:"markdown"`
	// Title is the level-one heading.
	Title string `json:"title"`
	// Phases are ordered and contiguous from 1.
	Phases []PlanPhase `json:"phases"`
	// References are the research ids the plan cites, deduplicated.
	References []string `json:"references,omitempty"`
}

// PlanPhase is one executable unit of the plan. Files and Changes are prose
// for the implementer; the verification entries are what Orchestra runs and
// what the human signs off.
type PlanPhase struct {
	// ID is the stable name used in a progress request, "phase-1".
	ID     string `json:"id"`
	Number int    `json:"number"`
	Name   string `json:"name"`
	// Body is the phase's markdown, retained so a mismatch report can quote it.
	Body string `json:"body"`
	// Automated are argv arrays. Not shell strings: they execute through
	// exec.Command with no shell, so a pipe or a redirection is a literal
	// argument rather than an operator.
	Automated [][]string `json:"automated,omitempty"`
	// Manual are human-testable steps. A phase whose automated checks all pass
	// while manual steps remain is awaiting a human, not verified.
	Manual []string `json:"manual,omitempty"`
}

const (
	// MaxPlanBytes bounds the whole document. A specification needs room that
	// the 500-character single-line rule never allowed, but an unbounded
	// artifact is a transcript that every later session pays to read.
	MaxPlanBytes = 128 << 10
	maxPhases    = 32
	maxCommands  = 16
	maxArgv      = 32
)

// requiredSections are the level-two headings every plan carries. They are the
// questions a plan has to answer before anyone implements against it: what is
// true now, what should be true after, and what is deliberately not being done.
var requiredSections = []string{
	"Overview", "Current state", "Desired end state", "Non-goals", "Approach",
	"Testing strategy", "Risks and edge cases", "Migration", "References",
}

var (
	phaseHeading = regexp.MustCompile(`^##\s+Phase\s+(\d+)\s*:\s*(.+?)\s*$`)
	runLine      = regexp.MustCompile(`^-\s+run:\s*(.+?)\s*$`)
	bulletLine   = regexp.MustCompile(`^[-*]\s+(.+?)\s*$`)
	researchCite = regexp.MustCompile(`research:([a-z0-9][a-z0-9_-]{0,63})`)
)

// ParsePlan reads a markdown plan and reports the first structural problem it
// finds. Errors name the section or phase, because "invalid plan" sends a
// planner rereading its own document with nothing to go on.
func ParsePlan(b []byte) (PlanDoc, error) {
	if len(b) == 0 {
		return PlanDoc{}, fmt.Errorf("plan: the document is empty")
	}
	if len(b) > MaxPlanBytes {
		return PlanDoc{}, fmt.Errorf("plan: %d bytes exceeds the %d byte bound", len(b), MaxPlanBytes)
	}
	doc := PlanDoc{Markdown: string(b)}
	lines := strings.Split(strings.ReplaceAll(doc.Markdown, "\r\n", "\n"), "\n")

	sections := map[string]bool{}
	// current tracks which phase's body the parser is inside, and which
	// verification subsection, so a "- run:" line is attributed to the phase
	// that actually contains it.
	var current *PlanPhase
	subsection := ""
	inFence := false

	flush := func() {
		if current != nil {
			current.Body = strings.TrimSpace(current.Body)
			doc.Phases = append(doc.Phases, *current)
			current = nil
		}
	}

	for n, raw := range lines {
		line := strings.TrimRight(raw, " \t")
		// A heading inside a fenced block is content, not structure. Without
		// this a plan that shows example markdown parses its own example.
		if strings.HasPrefix(strings.TrimSpace(line), "```") {
			inFence = !inFence
		}
		if !inFence {
			switch {
			case strings.HasPrefix(line, "# "):
				if doc.Title == "" {
					doc.Title = strings.TrimSpace(strings.TrimPrefix(line, "# "))
				}
				continue
			case phaseHeading.MatchString(line):
				flush()
				m := phaseHeading.FindStringSubmatch(line)
				number, _ := strconv.Atoi(m[1])
				current = &PlanPhase{ID: "phase-" + m[1], Number: number, Name: m[2]}
				subsection = ""
				continue
			case strings.HasPrefix(line, "## "):
				flush()
				sections[strings.TrimSpace(strings.TrimPrefix(line, "## "))] = true
				subsection = strings.TrimSpace(strings.TrimPrefix(line, "## "))
				continue
			case strings.HasPrefix(line, "#### "):
				subsection = strings.TrimSpace(strings.TrimPrefix(line, "#### "))
			case strings.HasPrefix(line, "### "):
				subsection = strings.TrimSpace(strings.TrimPrefix(line, "### "))
			}
		}
		if current == nil {
			continue
		}
		current.Body += line + "\n"
		if inFence {
			continue
		}
		switch subsection {
		case "Automated":
			m := runLine.FindStringSubmatch(line)
			if m == nil {
				continue
			}
			var argv []string
			if err := json.Unmarshal([]byte(m[1]), &argv); err != nil {
				return PlanDoc{}, fmt.Errorf("plan: %s line %d: run: must be a JSON argv array like [\"go\", \"test\", \"./...\"], got %s", current.ID, n+1, m[1])
			}
			if err := validArgv(current.ID, argv); err != nil {
				return PlanDoc{}, err
			}
			current.Automated = append(current.Automated, argv)
		case "Manual":
			if m := bulletLine.FindStringSubmatch(line); m != nil {
				current.Manual = append(current.Manual, m[1])
			}
		}
	}
	flush()

	if doc.Title == "" {
		return PlanDoc{}, fmt.Errorf("plan: a level-one heading naming the plan is required")
	}
	for _, name := range requiredSections {
		if !sections[name] {
			return PlanDoc{}, fmt.Errorf("plan: the %q section is required", name)
		}
	}
	if err := doc.validatePhases(); err != nil {
		return PlanDoc{}, err
	}
	doc.References = citations(doc.Markdown)
	return doc, nil
}

func (d PlanDoc) validatePhases() error {
	if len(d.Phases) == 0 {
		return fmt.Errorf("plan: at least one \"## Phase 1: <name>\" section is required")
	}
	if len(d.Phases) > maxPhases {
		return fmt.Errorf("plan: %d phases exceeds the %d phase bound", len(d.Phases), maxPhases)
	}
	for i, p := range d.Phases {
		// Contiguous numbering from 1. A plan that jumps from phase 2 to
		// phase 4 has either lost a phase or renumbered one that progress
		// already refers to, and both are worse discovered later.
		if p.Number != i+1 {
			return fmt.Errorf("plan: phases must be numbered from 1 with no gaps; found Phase %d where Phase %d was expected", p.Number, i+1)
		}
		if strings.TrimSpace(p.Name) == "" {
			return fmt.Errorf("plan: %s has no name", p.ID)
		}
		for _, required := range []string{"### Files", "### Changes", "### Verification"} {
			if !strings.Contains(p.Body, required) {
				return fmt.Errorf("plan: %s is missing its %q subsection", p.ID, strings.TrimPrefix(required, "### "))
			}
		}
		// A phase nobody can check is a phase that can never leave
		// in_progress, so it is refused at seal time rather than becoming a
		// stuck task later.
		if len(p.Automated) == 0 && len(p.Manual) == 0 {
			return fmt.Errorf("plan: %s has no automated and no manual verification, so nothing could ever establish it is done", p.ID)
		}
		if len(p.Automated) > maxCommands {
			return fmt.Errorf("plan: %s declares %d automated commands, at most %d", p.ID, len(p.Automated), maxCommands)
		}
	}
	return nil
}

func validArgv(phase string, argv []string) error {
	if len(argv) == 0 {
		return fmt.Errorf("plan: %s declares an empty run: command", phase)
	}
	if len(argv) > maxArgv {
		return fmt.Errorf("plan: %s declares a run: command of %d arguments, at most %d", phase, len(argv), maxArgv)
	}
	for i, a := range argv {
		if strings.TrimSpace(a) == "" {
			return fmt.Errorf("plan: %s run: argument %d is empty", phase, i)
		}
		if strings.ContainsAny(a, "\n\r\x00") {
			return fmt.Errorf("plan: %s run: argument %d contains a newline or a null byte", phase, i)
		}
	}
	return nil
}

// Phase finds a phase by its id.
func (d PlanDoc) Phase(id string) (PlanPhase, bool) {
	for _, p := range d.Phases {
		if p.ID == id {
			return p, true
		}
	}
	return PlanPhase{}, false
}

// citations returns every research id the document cites, deduplicated, in
// order of first appearance.
func citations(markdown string) []string {
	var out []string
	seen := map[string]bool{}
	for _, m := range researchCite.FindAllStringSubmatch(markdown, -1) {
		if !seen[m[1]] {
			seen[m[1]] = true
			out = append(out, m[1])
		}
	}
	return out
}

// ResolveReferences reports the cited research ids that the accepted research
// does not contain. A plan resting on a finding nobody recorded is the failure
// this prevents, and it lands on the planner rather than the implementer.
func (d PlanDoc) ResolveReferences(r Research) []string {
	known := map[string]bool{}
	for _, f := range r.Findings {
		known[f.ID] = true
	}
	var missing []string
	for _, id := range d.References {
		if !known[id] {
			missing = append(missing, id)
		}
	}
	return missing
}

// DecodeStoredPlan reads a plan already in the CAS. New seals are markdown;
// refs sealed before plan.md existed are JSON, and refusing them would block
// every task whose plan predates this change, at rotation most of all.
//
// A legacy plan is rendered into the same type so nothing downstream branches
// on which era a plan came from. It carries no phases, which is honest: the
// old artifact never named an executable unit, so plan progress genuinely
// cannot apply to it.
func DecodeStoredPlan(b []byte) (PlanDoc, error) {
	if doc, err := ParsePlan(b); err == nil {
		return doc, nil
	}
	p, err := DecodePlan(b)
	if err != nil {
		// Report the markdown failure, not the JSON one: every new seal is
		// markdown, so that is the error a reader needs.
		_, mdErr := ParsePlan(b)
		return PlanDoc{}, mdErr
	}
	return p.legacyDoc(), nil
}

// legacyDoc renders a pre-markdown plan as the document type. The text is
// labelled so nobody mistakes a flattened plan for a specification.
func (p Plan) legacyDoc() PlanDoc {
	var b strings.Builder
	b.WriteString("# Accepted plan\n\nSealed before plan.md existed, so it names intent rather than phases.\n\n## Changes\n\n")
	for _, c := range p.Changes {
		fmt.Fprintf(&b, "- %s: %s\n", c.Target, c.Intent)
	}
	for _, section := range []struct {
		title string
		items []string
	}{
		{"Verification", p.Verification},
		{"Risks", p.Risks},
		{"Human decisions needed", p.DecisionsNeeded},
	} {
		if len(section.items) == 0 {
			continue
		}
		fmt.Fprintf(&b, "\n## %s\n\n", section.title)
		for _, v := range section.items {
			fmt.Fprintf(&b, "- %s\n", v)
		}
	}
	return PlanDoc{Markdown: b.String(), Title: "Accepted plan"}
}