package tools

import (
	"context"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"

	"git.d-ma.be/mathias/gitea-mcp/internal/allowlist"
	"git.d-ma.be/mathias/gitea-mcp/internal/auth"
	"git.d-ma.be/mathias/gitea-mcp/internal/gitea"
	"git.d-ma.be/mathias/gitea-mcp/internal/identity"
	"git.d-ma.be/mathias/gitea-mcp/internal/registry"
)

// TBDShip is the intent verb for the trunk-based loop: branch → write → PR →
// (CI-green) auto-merge → clean up. The safety is the CI gate — it fails closed
// on anything that isn't a fully-green, unprotected, cleanly-mergeable change.
type TBDShip struct {
	c *gitea.Client
	a *allowlist.Allowlist
}

func NewTBDShip(c *gitea.Client, a *allowlist.Allowlist) *TBDShip { return &TBDShip{c: c, a: a} }

const (
	shipCIPollInterval  = 5 * time.Second
	shipCIMaxTimeoutSec = 600
)

func (t *TBDShip) Descriptor() registry.ToolDescriptor {
	return registry.ToolDescriptor{
		Name: "tbd_ship",
		Description: "Trunk-based ship of a single-file change: branch from base, write the file, open a PR, and auto-merge (squash) to base ONLY when the head commit's CI is fully green. Fails closed to PR-only (never merges) when CI is pending, red, or absent, when the base branch requires reviews, or when the merge isn't clean — returning the PR for manual handling with a reason. Set ci_timeout_seconds to poll CI to completion (default 0 = snapshot, which returns pending right after opening the PR). Returns {merged, pr_url, pr_number, ci_status, reason, branch}.",
		InputSchema: json.RawMessage(`{
			"type":"object",
			"properties":{
				"owner":{"type":"string"},
				"repo":{"type":"string"},
				"path":{"type":"string","description":"File path to create or update."},
				"content":{"type":"string","description":"Full file content (plain text)."},
				"message":{"type":"string","description":"Commit message."},
				"base":{"type":"string","description":"Base branch to ship to. Default 'main'."},
				"branch":{"type":"string","description":"Short-lived branch name. Default derived: tbd/<slug>-<hash>."},
				"pr_title":{"type":"string","description":"PR title. Default: the commit message."},
				"pr_body":{"type":"string"},
				"delete_branch":{"type":"boolean","description":"Delete the branch after a successful merge. Default true."},
				"ci_timeout_seconds":{"type":"integer","minimum":0,"maximum":600,"description":"Poll CI up to this long for the head commit's runs to complete. Default 0 (single snapshot)."}
			},
			"required":["owner","repo","path","content","message"]
		}`),
	}
}

type tbdShipArgs struct {
	Owner        string `json:"owner"`
	Repo         string `json:"repo"`
	Path         string `json:"path"`
	Content      string `json:"content"`
	Message      string `json:"message"`
	Base         string `json:"base"`
	Branch       string `json:"branch"`
	PRTitle      string `json:"pr_title"`
	PRBody       string `json:"pr_body"`
	DeleteBranch *bool  `json:"delete_branch"`
	CITimeoutSec int    `json:"ci_timeout_seconds"`
}

// shipGate is the decision produced by evaluateShipGate.
type shipGate struct {
	merge    bool
	ciStatus string // none | pending | failed | success
	reason   string // non-empty iff merge == false
}

// classifyCI reduces a set of workflow runs for one commit to a single status.
// Fail-closed: only "success" (all runs completed and successful) permits a
// merge; anything else — no runs, still-running, or any non-success conclusion
// (failure/cancelled/skipped) — blocks it.
func classifyCI(runs []gitea.WorkflowRun) string {
	if len(runs) == 0 {
		return "none"
	}
	for _, r := range runs {
		if r.Status != "completed" {
			return "pending"
		}
	}
	for _, r := range runs {
		if r.Conclusion != "success" {
			return "failed"
		}
	}
	return "success"
}

// evaluateShipGate is the load-bearing safety of tbd_ship. It returns merge=true
// only when CI is fully green AND the base branch is not review-protected. Every
// other state fails closed to PR-only with an explanatory reason (#40).
func evaluateShipGate(runs []gitea.WorkflowRun, bp *gitea.BranchProtection) shipGate {
	ci := classifyCI(runs)

	// Review-protected base can't be auto-merged regardless of CI.
	if bp != nil && bp.Protected && bp.RequiredApprovals > 0 {
		return shipGate{false, ci, fmt.Sprintf(
			"base branch requires %d approving review(s) — auto-merge disabled; PR opened for manual merge", bp.RequiredApprovals)}
	}

	switch ci {
	case "success":
		return shipGate{true, ci, ""}
	case "pending":
		return shipGate{false, ci, "CI is still running for the head commit — PR opened; re-invoke once checks complete, or merge manually"}
	case "failed":
		return shipGate{false, ci, "CI failed for the head commit — PR opened, not merged"}
	default: // none
		return shipGate{false, ci, "no CI runs found for the head commit — fail-closed: a change with no CI gate is never auto-merged to trunk; PR opened for manual merge"}
	}
}

var shipSlugRe = regexp.MustCompile(`[^a-z0-9]+`)

// deriveBranch builds a deterministic short-lived branch name from the change,
// so the same change maps to the same branch and distinct changes don't collide.
func deriveBranch(message, path, content string) string {
	slug := strings.Trim(shipSlugRe.ReplaceAllString(strings.ToLower(message), "-"), "-")
	if len(slug) > 32 {
		slug = strings.Trim(slug[:32], "-")
	}
	if slug == "" {
		slug = "change"
	}
	sum := sha256.Sum256([]byte(path + "\x00" + content + "\x00" + message))
	return "tbd/" + slug + "-" + hex.EncodeToString(sum[:])[:8]
}

func (t *TBDShip) Call(ctx context.Context, raw json.RawMessage) (json.RawMessage, error) {
	var args tbdShipArgs
	if err := parseArgs(raw, &args); err != nil {
		return nil, err
	}
	if err := t.a.Check(args.Owner); err != nil {
		return nil, err
	}
	if args.Path == "" || args.Content == "" || args.Message == "" {
		return nil, fmt.Errorf("path, content, and message are required: %w", gitea.ErrValidation)
	}

	base := args.Base
	if base == "" {
		base = "main"
	}
	branch := args.Branch
	if branch == "" {
		branch = deriveBranch(args.Message, args.Path, args.Content)
	}
	deleteBranch := true
	if args.DeleteBranch != nil {
		deleteBranch = *args.DeleteBranch
	}

	// Probe base-branch protection up front — a real error fails closed.
	bp, err := t.c.GetBranchProtection(ctx, args.Owner, args.Repo, base)
	if err != nil {
		return nil, fmt.Errorf("branch protection probe: %w", err)
	}

	// Branch from base, write the change, open the PR.
	if err := t.c.CreateBranch(ctx, args.Owner, args.Repo, branch, base); err != nil {
		return nil, fmt.Errorf("create branch %s: %w", branch, err)
	}

	// A pre-existing file at path needs its blob sha to update; a new file does not.
	sha := ""
	if fc, ferr := t.c.GetFileContents(ctx, args.Owner, args.Repo, args.Path, branch); ferr == nil {
		sha = fc.Sha
	} else if !errors.Is(ferr, gitea.ErrNotFound) {
		return nil, fmt.Errorf("read %s on %s: %w", args.Path, branch, ferr)
	}
	if _, err := t.c.UpsertFile(ctx, args.Owner, args.Repo, args.Path, gitea.UpsertFileArgs{
		Branch:  branch,
		Content: base64.StdEncoding.EncodeToString([]byte(args.Content)),
		Message: args.Message,
		Sha:     sha,
	}); err != nil {
		return nil, fmt.Errorf("write %s on %s: %w", args.Path, branch, err)
	}

	prTitle := args.PRTitle
	if prTitle == "" {
		prTitle = args.Message
	}
	pr, err := t.c.CreatePullRequest(ctx, args.Owner, args.Repo, gitea.CreatePullRequestArgs{
		Title: prTitle,
		Body:  identity.ApplyFooter(args.PRBody, auth.Caller(ctx)),
		Head:  branch,
		Base:  base,
	})
	if err != nil {
		return nil, fmt.Errorf("open PR: %w", err)
	}

	// CI gate on the PR head commit.
	runs := t.pollRuns(ctx, args.Owner, args.Repo, pr.Head.Sha, args.CITimeoutSec)
	gate := evaluateShipGate(runs, bp)

	result := map[string]any{
		"merged":    false,
		"pr_number": pr.Number,
		"pr_url":    pr.HTMLURL,
		"branch":    branch,
		"ci_status": gate.ciStatus,
	}
	if !gate.merge {
		result["reason"] = gate.reason
		return textOK(result)
	}

	// Green + unprotected → squash-merge, then delete the short-lived branch.
	if err := t.c.MergePullRequest(ctx, args.Owner, args.Repo, pr.Number, gitea.MergePRArgs{Do: "squash"}); err != nil {
		if errors.Is(err, gitea.ErrConflict) {
			result["reason"] = "base moved and the merge is not clean — PR opened, not merged; resolve the conflict and merge manually"
			return textOK(result)
		}
		return nil, fmt.Errorf("merge PR #%d: %w", pr.Number, err)
	}
	result["merged"] = true
	if deleteBranch {
		if derr := t.c.DeleteBranch(ctx, args.Owner, args.Repo, branch); derr == nil {
			result["branch_deleted"] = true
		}
	}
	return textOK(result)
}

// pollRuns lists the head commit's workflow runs, polling up to timeoutSec for
// them to reach a terminal state. timeoutSec == 0 is a single snapshot (no
// sleep). A listing error yields no runs → the gate fails closed.
func (t *TBDShip) pollRuns(ctx context.Context, owner, repo, headSHA string, timeoutSec int) []gitea.WorkflowRun {
	if timeoutSec < 0 {
		timeoutSec = 0
	}
	if timeoutSec > shipCIMaxTimeoutSec {
		timeoutSec = shipCIMaxTimeoutSec
	}
	deadline := time.Now().Add(time.Duration(timeoutSec) * time.Second)
	for {
		runs := t.listRuns(ctx, owner, repo, headSHA)
		switch classifyCI(runs) {
		case "success", "failed":
			return runs // terminal — no point waiting
		}
		if time.Now().After(deadline) {
			return runs // out of time — return whatever we have (none/pending)
		}
		select {
		case <-ctx.Done():
			return runs
		case <-time.After(shipCIPollInterval):
		}
	}
}

func (t *TBDShip) listRuns(ctx context.Context, owner, repo, headSHA string) []gitea.WorkflowRun {
	resp, err := t.c.ListWorkflowRuns(ctx, owner, repo, gitea.ListWorkflowRunsArgs{HeadSHA: headSHA, Limit: 50})
	if err != nil || resp == nil {
		return nil
	}
	return resp.WorkflowRuns
}