// Copyright 2026 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package task

import (
	"bytes"
	stdctx "context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"

	"gitea.dev/tea/modules/api"
	"gitea.dev/tea/modules/config"
	"gitea.dev/tea/modules/stack"
)

func stackAPIError(resp *http.Response) error {
	data, err := io.ReadAll(resp.Body)
	if err != nil {
		return fmt.Errorf("body read on HTTP error %d: %w", resp.StatusCode, err)
	}

	var errBody struct {
		Message string `json:"message"`
	}
	if err := json.Unmarshal(data, &errBody); err == nil && errBody.Message != "" {
		return fmt.Errorf("%s", errBody.Message)
	}
	return fmt.Errorf("%s: %s", resp.Status, string(data))
}

func decodeStackResponse(resp *http.Response, wantStatus int, out any) error {
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode != wantStatus {
		return stackAPIError(resp)
	}
	if out == nil {
		return nil
	}
	return json.NewDecoder(resp.Body).Decode(out)
}

// pullStackLinkOption links a parent and a child pull request in the same repository.
type pullStackLinkOption struct {
	ParentIndex int64 `json:"parent_index"`
	ChildIndex  int64 `json:"child_index"`
}

func postStackJSON(ctx stdctx.Context, login *config.Login, endpoint string, body any, wantStatus int, out any) error {
	client := api.NewClient(login)

	var reader io.Reader
	if body != nil {
		encoded, err := json.Marshal(body)
		if err != nil {
			return err
		}
		reader = bytes.NewReader(encoded)
	}

	resp, err := client.DoContext(ctx, http.MethodPost, endpoint, reader, nil)
	if err != nil {
		return err
	}
	return decodeStackResponse(resp, wantStatus, out)
}

// ListPullStacks lists the pull request stacks of a repository.
func ListPullStacks(ctx stdctx.Context, login *config.Login, owner, repo string) ([]*stack.Stack, error) {
	client := api.NewClient(login)
	resp, err := client.DoContext(ctx, http.MethodGet, fmt.Sprintf("/repos/%s/%s/stacks", owner, repo), nil, nil)
	if err != nil {
		return nil, err
	}

	var stacks []*stack.Stack
	if err := decodeStackResponse(resp, http.StatusOK, &stacks); err != nil {
		return nil, err
	}
	return stacks, nil
}

// GetPullStack retrieves one stack with its ordered pull requests.
func GetPullStack(ctx stdctx.Context, login *config.Login, owner, repo string, id int64) (*stack.Stack, error) {
	client := api.NewClient(login)
	resp, err := client.DoContext(ctx, http.MethodGet, fmt.Sprintf("/repos/%s/%s/stacks/%d", owner, repo, id), nil, nil)
	if err != nil {
		return nil, err
	}

	var s stack.Stack
	if err := decodeStackResponse(resp, http.StatusOK, &s); err != nil {
		return nil, err
	}
	return &s, nil
}

// CreatePullStack explicitly links two same-repository pull requests, forming a new stack.
func CreatePullStack(ctx stdctx.Context, login *config.Login, owner, repo string, parentIndex, childIndex int64) (*stack.Stack, error) {
	var s stack.Stack
	err := postStackJSON(ctx, login, fmt.Sprintf("/repos/%s/%s/stacks", owner, repo),
		pullStackLinkOption{ParentIndex: parentIndex, ChildIndex: childIndex}, http.StatusCreated, &s)
	if err != nil {
		return nil, err
	}
	return &s, nil
}

// AddPullStackEntry appends one pull request to the tip of an existing stack.
func AddPullStackEntry(ctx stdctx.Context, login *config.Login, owner, repo string, id, parentIndex, childIndex int64) (*stack.Stack, error) {
	var s stack.Stack
	err := postStackJSON(ctx, login, fmt.Sprintf("/repos/%s/%s/stacks/%d/entries", owner, repo, id),
		pullStackLinkOption{ParentIndex: parentIndex, ChildIndex: childIndex}, http.StatusCreated, &s)
	if err != nil {
		return nil, err
	}
	return &s, nil
}

// ReorderPullStack records the order of PR branches that are already linked.
func ReorderPullStack(ctx stdctx.Context, login *config.Login, owner, repo string, id int64, pullIndices []int64) (*stack.Stack, error) {
	var s stack.Stack
	err := postStackJSON(ctx, login, fmt.Sprintf("/repos/%s/%s/stacks/%d/reorder", owner, repo, id),
		struct {
			PullIndices []int64 `json:"pull_indices"`
		}{PullIndices: pullIndices}, http.StatusOK, &s)
	if err != nil {
		return nil, err
	}
	return &s, nil
}

// RestackPullStack queues a restack starting at the stack's base branch.
func RestackPullStack(ctx stdctx.Context, login *config.Login, owner, repo string, id int64) error {
	client := api.NewClient(login)
	resp, err := client.DoContext(ctx, http.MethodPost, fmt.Sprintf("/repos/%s/%s/stacks/%d/restack", owner, repo, id), nil, nil)
	if err != nil {
		return err
	}
	return decodeStackResponse(resp, http.StatusAccepted, nil)
}

type pullStackMergeOption struct {
	Style     string `json:"style"`
	WaitForCI bool   `json:"wait_for_ci"`
}

// MergePullStack merges every pull request of a stack in order. If waitForCI is set, the merge is
// scheduled instead of applied immediately and MergePullStack returns with queued=true. Otherwise
// it returns the number of pull requests merged; a non-nil error means the merge stopped partway,
// with result.Merged reporting how many pull requests succeeded before that.
func MergePullStack(ctx stdctx.Context, login *config.Login, owner, repo string, id int64, style string, waitForCI bool) (result *stack.MergeResult, queued bool, err error) {
	client := api.NewClient(login)
	encoded, err := json.Marshal(pullStackMergeOption{Style: style, WaitForCI: waitForCI})
	if err != nil {
		return nil, false, err
	}

	resp, err := client.DoContext(ctx, http.MethodPost, fmt.Sprintf("/repos/%s/%s/stacks/%d/merge", owner, repo, id),
		bytes.NewReader(encoded), nil)
	if err != nil {
		return nil, false, err
	}
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode == http.StatusAccepted {
		return nil, true, nil
	}
	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusConflict {
		return nil, false, stackAPIError(resp)
	}

	var body stack.MergeResult
	if decodeErr := json.NewDecoder(resp.Body).Decode(&body); decodeErr != nil {
		return nil, false, fmt.Errorf("%s: failed to decode response: %w", resp.Status, decodeErr)
	}
	if resp.StatusCode != http.StatusOK {
		if body.Error == "" {
			return &body, false, fmt.Errorf("%s", resp.Status)
		}
		return &body, false, fmt.Errorf("%s", body.Error)
	}
	return &body, false, nil
}