[BE-97] Asset depreciation calculation

[yusuftomilola]

Overview

The frontend has depreciation charts planned ([FE-23] in the existing backlog) and categories carry depreciation defaults ([BE-85]). Book value drives audit and financial reporting.

Tasks

• Add depreciation fields to assets: method (STRAIGHT_LINE/DECLINING_BALANCE/NONE), usefulLifeMonths, salvageValue, depreciationStartDate — inheriting category defaults.
• Implement calculation for each method; expose current book value, accumulated depreciation, and a period-by-period schedule.
• Add GET /assets/${id}/depreciation returning the schedule, and a portfolio-wide total book value for reports.
• Use integer minor units throughout and define the rounding rule explicitly — document who absorbs the remainder.
• Handle edge cases: disposal mid-life, zero useful life, salvage exceeding cost.
• Write tests with worked examples verified by hand.

Acceptance Criteria

• Straight-line and declining-balance figures match hand-calculated examples exactly.
• Book value never falls below salvage value.
• Rounding is deterministic and documented.

Dependencies

Blocked by [BE-85] and [BE-86].

Notes for Contributors

The backend is being rebuilt from a clean NestJS skeleton — backend/src/ currently contains only app.module.ts, app.controller.ts, app.service.ts, and main.ts. Follow standard NestJS module structure (module / controller / service / dto / entities) and register your module in app.module.ts. Comment below to be assigned.

[toniasteve15-ui]

@toniasteve15-ui has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer, reviewed the issue in detail. Full stack background with solid experience relevant to this task. No blockers on my end — I'm ready to submit a PR shortly. Please assign.

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[NeduTheDev1]

@NeduTheDev1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Please assign to me maintainer I can handle with no issues

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[Kaizer4show]

@Kaizer4show has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi maintainer, I would like to work on this issue please

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[Userhorlie]

@Userhorlie has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I'd like to take this on.

The frontend has depreciation charts planned ([FE-23] in the existing backlog) and categories carry depreciation defaults ([BE-85]). Book value drives audit and financial reporting.

I'll make sure each of these is covered:

• Straight-line and declining-balance figures match hand-calculated examples exactly
• Book value never falls below salvage value
• Rounding is deterministic and documented
• Dependencies

I'll keep you posted on progress as I go.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Userhorlie to this issue.

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Congratulations, @Userhorlie! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

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[grantfox-oss]

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@Userhorlie's PR #1233 was approved and merged by @yusuftomilola.

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👏 Great work, @Userhorlie! Keep contributing to DistinctCodes.

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This issue has been completed by @Userhorlie as part of the Stellar Wave Program's 7th Wave 🥳

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